This invention relates to a method for purifying contaminated oil which contains solids and water. More specifically, the present invention concerns purification of an oil contaminated with solids and water and which forms a solids-stabilized emulsion.
Oil streams contaminated with large amounts of particulate solids and emulsified water are formed during many petroleum refining operations. Common sources of such oil, sometimes termed "slop oil" are separation operations, desalting operations, other oil washing operations, equipment drainage and washing operations, froth from flotation type water purification, etc. The solids and water contained in such slop oil are sometimes referred to as bottoms sediments and water ("BS&W").
Oil which is contaminated with dispersed solids and emulsified water is usually treated by settling it in a large storage tank until it separates into an oil layer, an intermediate layer and a lower water layer. The intermediate layer, sometimes termed an "oil cuff", is a difficult to treat, stable emulsion of oil, water and particulate solids. Typically, simply settling contaminated oil in the conventional manner to provide the three layers, has the disadvantages of (1) requiring a relatively long period of settling to accomplish adequate separation of water and solids from the oil, (2) providing oil and water layers which are not as free from contaminants as is desired, and (3) resulting in formation of an overly large oil cuff layer containing too large a proportion of the original contaminated oil. Better separation has been attempted by heating the oil during settling and by adding demulsifiers to the oil; however, many contaminated oils contain solids-stabilized, oil-water emulsions which are quite difficult to break. The present invention is directed, in part, toward providing a more efficient and practical way to separate water and solids from contaminated oil.